Ultra wideband modulation for body area networks

ABSTRACT

A symbol modulation system applicable to a body area network is disclosed herein. The symbol modulation system includes a symbol mapper. The symbol mapper is configured to determine a time within a predetermined symbol transmission interval at which a transmission representative of the symbol will occur. The time is determined based on a value of a symbol and a value of a time-hopping sequence. The time is selected from a plurality of symbol value based time slots, and a plurality of time-hopping sequence sub-time-slots within each symbol value based time slot. The symbol mapper is configured to generate a single guard interval within the symbol transmission interval. The single guard interval is positioned to terminate the symbol transmission interval.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/074,448,filed Nov. 7, 2013, which is a division of application Ser. No.12/702,628, filed Feb. 9, 2010 (now U.S. Pat. No. 8,605,770), which is anon-provisional application claiming priority to Provisional ApplicationNo. 61/151,007, filed Feb. 9, 2009, and to Provisional Application No.61/240,760, filed Sep. 9, 2009, all of which are incorporated byreference herein.

BACKGROUND

Body area networks (BAN) are a low-power short-range wireless technologythat can be used for medical applications, such a digital band-aids andpacemakers, and for entertainment and consumer electronics applications,including heads-up displays and wireless gaming.

Body area networks are being designed for use in several radio frequencybands, including 400 MHz Medical Implant Communications Service (“MICS”)band, 900 MHz and 2.4 GHz Industrial, Scientific and Medical (“ISM”)band, and 3.1-10.6 GHz Ultra Wideband (UWB) band.

SUMMARY

A symbol modulation system applicable to a body area network isdisclosed herein. In accordance with some embodiments, a symbolmodulation system includes a symbol mapper. The symbol mapper isconfigured to determine a time within a predetermined symboltransmission interval at which a transmission representative of thesymbol will occur. The time is determined based on a value of a symboland a value of a time-hopping sequence. The time is selected from aplurality of symbol value based time slots, and a plurality oftime-hopping sequence sub-time-slots within each symbol value based timeslot. The symbol mapper is further configured to generate a single guardinterval within the symbol transmission interval. The single guardinterval is positioned to terminate the symbol transmission interval.

In accordance with at least some other embodiments, a method includesdetermining, by a symbol mapping circuit, a time within a predeterminedsymbol transmission interval at which a burst of pulses representativeof a symbol to be transmitted will be occur. The determination is basedon a value of the symbol and a value of a time-hopping sequence. Thesymbol mapping circuit also generates a single guard interval thatterminates the transmission interval. The determined time is selectedfrom a plurality of symbol value based time slots, and a plurality oftime-hopping sequence sub-time-slots within each symbol value based timeslot.

In accordance with yet other embodiments, a body area network includesan impulse radio ultra-wideband (“IR-UWB”) transmitter and an IR-UWBreceiver. The transmitter is configured to apply burst positionmodulation exclusively, and to apply a single guard interval period persymbol transmitted. The IR-UWB receiver is configured to receivetransmissions of the ultra-wideband impulse-radio transmitter. The ratioof the guard interval period to a symbol transmission period is reducedas a data rate used to transmit the symbol decreases.

In accordance with some additional embodiments, a symbol modulationsystem includes a symbol mapper. The symbol mapper is configured todetermine, based on a value of a time-hopping sequence, a time within apredetermined symbol transmission interval at which a signal burstrepresentative of the symbol will be transmitted. The symbol mapper isalso configured to determine, based on a value of the symbol, amodulation factor to apply to the signal burst during the time. Thesymbol mapper is further configured to generate a single guard intervalwithin the symbol transmission interval. The time is selected from aplurality of time-hopping sequence time-slots within the predeterminedsymbol transmission interval. The single guard interval is positioned toterminate the symbol transmission interval.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the invention,reference will now be made to the accompanying drawings in which:

FIG. 1 shows a representative Body Area Network (“BAN”) in accordancewith various embodiments;

FIG. 2 shows a block diagram for a portion of an Impulse RadioUltra-Wideband (“IR-UWB”) transmitter in accordance with variousembodiments;

FIGS. 3A and 3B shows the structure of a symbols generated by an IR-UWBmodulator in accordance with various embodiments; and

FIG. 4 shows a flow diagram for a method of IR-UWB modulation inaccordance with various embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” Also, the term “couple” or “couples” is intended tomean either an indirect or direct electrical connection. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections. The term “software”includes any executable code capable of running on a processor,regardless of the media used to store the software. Thus, code stored inmemory (e.g., non-volatile memory), and sometimes referred to as“embedded firmware,” is included within the definition of software. The“order” of a symbol is the number of values representable by the symbol(e.g., a binary (one-bit) symbol is of order 2, a quaternary (2-bit)symbol is of order 4, an M-ary symbol is of order M).

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

The physical layer (“PHY”) portion of a transceiver operates to convertsymbols (e.g., bits) to transmittable signals, and to convert receivedsignals into symbols. PHY design should consider channelcharacteristics. Embodiments of the present disclosure include animpulse-radio ultra-wideband (“IR-UWB”) PHY tailored for use with a bodyarea network (“BAN”).

FIG. 1 shows a representative BAN 100 in accordance with variousembodiments. The BAN 100 includes one or more nodes 102 A/B/C and a hub106. A node 102 may include a sensor (e.g., motion, temperature,electrical activity sensor, etc.), a processor, an output device (e.g.,audio or video transducers), etc. Each node 102 and the hub 106 mayinclude a transceiver 104 that communicatively couples the node 102 toone or more other nodes 102 and/or to the hub 106. Embodiments of thetransceiver 104 are configured for communication over relatively shortdistances applicable to the BAN 100. For example, the distance betweenthe hub 106 and any node 102 A/B/C may be three meters or less in theBAN 100.

The transceiver 104 includes a PHY configured for use in the BAN 100.Embodiments of the PHY use pulse position modulation (“PPM”). Someembodiments use PPM in conjunction with a different modulationtechnique, such as binary phase shift keying (“BPSK”). Other embodimentsuse PPM exclusively, thereby reducing implementation complexity whencompared to embodiments using PPM in combination with another modulationtechnique. Some embodiments of the PHY use a channel bandwidth of 512mega-hertz (“MHz”) or 528 MHz, with center frequencies that enable alow-power transceiver 104 architecture.

Embodiments of the PHY insert a single guard interval at the end of asymbol period. The guard interval is a fixed period and its length isdetermined by maximum delay spread of channel. Thus, the ratio of guardinterval to the symbol period changes as the data rate changes. Inparticular, the ratio of guard interval to symbol period decreases asthe data rate is decreased. By using this symbol structure, the numberof bursts per symbol may also be increased when compared to anembodiment allocating two guard intervals per symbol period, whichresults in enhanced interference mitigation. Alternatively, this symbolstructure allows for an increase in data rate while maintaining the sameburst length as an embodiment allocating two guard intervals per symbolperiod.

FIG. 2 shows a block diagram for a PHY portion of an IR-UWB transmitter200 in accordance with various embodiments. The PHY includes a scrambler202, a forward error correction (“FEC”) encoder 204, a symbol mapper206, a pulse generator 208, radio frequency (“RF”) circuitry 210, and anantenna 212. The scrambler 202 is a randomizing system used to eliminatelong runs of identical symbols. The scrambler 202 may be implemented,for example, as either a side-stream scrambler (e.g., per IEEE 802.11aor ECMA-368) or a self-synchronizing scrambler (e.g., per IEEE 802.11b).

The FEC encoder 204 adds redundancy to the transmitted symbols, therebyallowing a receiver to identify and correct channel induced errors inreceived data. As shown below in Tables 5-6, the PHY of the presentdisclosure supports both coded and uncoded data rates.

The symbol mapper 206 maps a scrambled/encoded input symbol to a signalrepresentative of the symbol. More specifically, the symbol mapper 206determines the position of the symbol in the time-domain, i.e., PPM. Thesymbol mapper 206 also determines the time-hopping sequence applied tothe symbol, and the polarities (or other parameters) of the pulses (peran applicable spreading sequence applied to the pulses) or otherwaveforms used to represent the symbol.

The symbol mapper 206 generates a single guard interval at the end ofeach symbol transmission. In some embodiments, the guard interval is afixed period and its length is determined based on maximum delay spreadof channel. Therefore, the ratio of guard interval to symbol periodchanges as the data rate changes.

The pulse generator 208 generates pulses at the time and with thepolarities specified by the symbol mapper 206. In some embodiments, thepulse generator 208 generates pulses having a width of approximately 2nano-seconds (“ns”). In other embodiments, the pulse generator 208generates pulses of a different width or other waveforms (e.g., achirp).

The RF circuitry 210 drives the output of the pulse generator 208 ontothe antenna 212 for conversion from conducted to an airwave form.

The scrambler 202, the FEC encoder 204, and the symbol mapper 206 may beimplemented in the digital domain by dedicated circuitry, processorsexecuting software programming, or a combination of the two. The pulsegenerator 208 can be implemented in either the analog or the digitaldomain, but in some embodiments, implementation in the analog domain isadvantageous for power reasons.

FIG. 3A shows the structure of a symbol generated by an IR-UWBtransmitter 200 in accordance with various embodiments. Symbol timeT_(S) is the interval of time occupied by one symbol. For an un-codedsystem, symbol rate is given by R_(S)=1/T_(S). When an FEC code is used,the symbol rate is R_(S)=1/T_(S)=R_(b)/r, where R_(b) is the data ratein bits per second and r is the code rate.

A guard interval of length T_(GI) is reserved at the end of each symbolas shown in FIG. 3A. The guard interval may be set to a value greaterthan the maximum delay spread of the channel in order to minimize theinter-symbol interference (“ISI”). As a result, the ratio of guardinterval to the symbol time becomes smaller as data rate decreases.

The symbol time excluding the guard interval is then divided intoN_(burst)=2N_(hop) slots, where each slot is of length T_(burst). Thatis, T_(S)=2N_(hop)T_(burst)+T_(GI). The slot time (or burst time) is aninteger multiple of the chip time T_(c). That is,T_(burst)=N_(cpb)T_(c), where N_(cpb) is the number of chips per burst.The chip time T_(c) is approximately 2 ns in some embodiments. Otherembodiments use a different chip time.

Within a symbol, N_(cpb) pulses are transmitted consecutively (in aburst manner) during a single selected time slot, while no signal istransmitted during the remaining (2N_(hop)−1) slots and the guardinterval. The time slot on which the pulse burst is transmitted duringthe k-th symbol interval is determined by the following two pieces ofinformation: (1) the data symbol d^((k)), and (2) the time-hopping(“TH”) sequence h^((k))ε{0, 1, . . . , N_(hop)−1}.

The data symbol is modulated onto the selected burst position (i.e.,burst position modulation). Note that the burst positions for a symbol“0” and a symbol “1” are separated by T_(BPM)=N_(hop)T_(burst). The THsequence h^((k))ε{0, 1, . . . , N_(hop)−1} is changing across symbols,and its value (in conjunction with the data symbol value) determines thetime slot during which the pulse burst is transmitted. The polarities ofthe pulses within the pulse burst are modulated using a chip scramblingsequence (or direct-sequence (“DS”) spreading sequence), c_(kN) _(cpbn)_(+n) ε{−1,1}. This modulation scheme may be called binary burstmodulation (“BPM”) with TH and DS, or more compactly, “BPM-TH/DS.”

More precisely, the transmit signal during the k-th symbol interval maybe expressed as:

${x^{(k)}(t)} = {\sum\limits_{n = 0}^{N_{cpb} - 1}\; {c_{{kN}_{cpb} + n}{p\left( {t - {d^{(k)}T_{BPM}} - {h^{(k)}T_{burst}} - {nT}_{c}} \right)}}}$

where

-   -   p(t): the transmitted pulse shape at the antenna input,    -   c_(kN) _(cpbn) _(+n) ε{−1,1}, n=0, 1, . . . , N_(cpb)−1: the        chip scrambling code (or DS spreading sequence) used during the        k-th symbol interval,    -   d^((k))ε{0,1}: the k-th data symbol carrying information,    -   h^((k))ε{0, 1, . . . , N_(hop)−1}: the time-hopping position for        the burst during the k-th symbol interval,    -   N_(cpb): the number of chips per burst,    -   T_(BPM)=N_(hop)T_(burst),    -   T_(burst)=N_(cpb)T_(c): slot time (or burst time),    -   T_(c): chip time.

The time-hopping sequence h^((k)) provides some immunity from multi-userinterference. The chip scrambling sequence c_(kN) _(cpbn) _(+n) providesadditional interference suppression as well as spectral smoothing of thetransmitted waveform.

In some embodiments, the time-hopping sequence h^((k)) and the chipscrambling sequence c_(kN) _(cpbn) _(+n) can be generated by using alinear feedback shift register (LFSR). There are various ways togenerate these sequences, including reading them from memory.

For embodiments using M-ary PPM, the symbol time excluding the guardinterval is divided into N_(burst)=MN_(hop) slots, where each slot is oflength T_(burst). That is T_(s), =MN_(hop)T_(burst)+T_(GI). The slottime (or burst time) is an integer multiple of the chip time T_(c). Thatis, T_(burst)=N_(cpb)T_(c), where N_(cpb) is the number of chips perburst. The transmit signal during the k-th symbol interval may beexpressed as:

${x^{(k)}(t)} = {\sum\limits_{n = 0}^{N_{cpb} - 1}\; {c_{{kN}_{cpb} + n}{p\left( {t - {d^{(k)}T_{BPM}} - {h^{(k)}T_{burst}} - {nT}_{c}} \right)}}}$

where

-   -   p(t): the transmitted pulse shape at the antenna input,    -   c_(kN) _(cpbn) _(+n) ε{−1,1}, n=0, 1, . . . , N_(cpb)−1: the        chip scrambling code (or DS spreading sequence) used during the        k-th symbol interval,    -   d^((k))ε{0, 1, . . . , M−1}: the k-th data symbol carrying        information,    -   h^((k))ε{0, 1, . . . , N_(hop)−1}: the time-hopping position for        the burst during the k-th symbol interval,    -   N_(cpb): the number of chips per burst,    -   T_(BPM)=N_(hop)T_(burst),    -   T_(burst)=N_(cpb)T_(c): slot time (or burst time),    -   T_(c): chip time.

FIG. 3B shows the structure of a symbol generated by an IR-UWBtransmitter 200 configured for on/off keying (“OOK”), pulse amplitudemodulation (“PAM”) or (differential) phase-shift keying (“PSK”)including (differential) binary PSK (“BPSK”) in accordance with variousembodiments. The symbol time excluding the guard interval is dividedinto N_(burst)=N_(hop) slots, where each slot is of length T_(burst).That is T_(s)=N_(hop)T_(burst)+T_(GI). The slot time (or burst time) isan integer multiple of the chip time T_(c). That is,T_(burst)=N_(cpb)T_(c), where N_(cpb) is the number of chips per burst.

The transmit signal during the k-th symbol interval may be expressed asshown:

${x^{(k)}(t)} = {s^{(k)}{\sum\limits_{n = 0}^{N_{cpb} - 1}\; {c_{{kN}_{cpb} + n}{p\left( {t - {h^{(k)}T_{burst}} - {nT}_{c}} \right)}}}}$

where

-   -   s^((k)): the k-th data symbol carrying information, more        specifically        -   OOK: s^((k))ε{0,1}, one is selected depending on information            data to transmit        -   PAM: s^((k))ε{0, 1, . . . , M−1}, one is selected depending            on information data to transmit        -   BPSK: s^((k))ε{−1,1}, one is selected depending on            information data to transmit        -   PSK:

$s^{(k)} \in \left\{ {{{{\exp \left( {\frac{{j2\pi}\; p}{M} + \varphi} \right)}\text{:}\mspace{14mu} p} = 0},1,\ldots \mspace{14mu},{M - 1}} \right\}$

-   -   -    where φ is a constant phase, one is selected depending on            the data symbol        -   Differential PSK has a form of s^((k))=s^((k))exp(jφ_(k)),            where φ_(k) changes depending on the k-th information data            to transmit.

    -   p(t): the transmitted pulse shape at the antenna input,

    -   c_(kN) _(cpbn) _(+n) ε{−1,1}, n=0, 1, . . . , N_(cpb)−1: the        chip scrambling code (or DS spreading sequence) used during the        k-th symbol interval,

    -   h^((k))ε{0, 1, . . . , N_(hop)−1}: the time-hopping position for        the burst during the k-th symbol interval,

    -   N_(cpb): the number of chips per burst,

    -   T_(burst)=N_(cpb)T_(c): slot time (or burst time),

    -   T_(c): chip time.

FIG. 4 shows a flow diagram for a method of IR-UWB modulation inaccordance with various embodiments. Though depicted sequentially as amatter of convenience, at least some of the actions shown can beperformed in a different order and/or performed in parallel.Additionally, some embodiments may perform only some of the actionsshown. In some embodiments, the operations of FIG. 4, as well as otheroperations described herein, can be implemented, at least in part, asinstructions stored in a computer readable medium and executed by aprocessor.

In block 402, the scrambler 202 randomizes the input symbol to eliminatelong sequences of like symbols. Various scrambling techniques may beemployed. For example, a self-synchronous scrambler or a side-streamscrambler may be used. A self-synchronous scrambler is a scramblerwhereby the current state of the scrambler is derived from the priorbits of the scrambled output. Consequently, the descrambler can acquirethe correct state directly from the received stream. A side-streamscrambler is a scrambler in which the current state of the scrambler isdependent only on the prior state of the scrambler and not on thetransmitted data. Therefore, the descrambler must acquire state eitherby searching for a state that decodes a known pattern or by agreement tostart at a known state in synchronization with the scrambler.

In block 404, the FEC encoder encodes the scrambled symbol (e.g., ablock of scrambled symbols) to provide redundancy that allows an FECdecoder in the receiver to detect and correct at least some posttransmission errors. Some embodiments of the PHY may employ a block code(e.g., a Bose-Chaudhuri-Hocquenghem or Reed-Solomon code). Embodimentsare not limited to any particular method of FEC coding.

In block 406, the symbol mapper 206 determines the location of thesymbol in the time domain, at what point in time a signal burstrepresenting the symbol will be generated. Referring to FIG. 3A, thesymbol mapper 206 determines, based on the symbol value to betransmitted, whether a burst will be generated in the “0” or “1” symbolvalue defined time slots of the symbol time T_(S).

In block 408, the symbol mapper 206 determines the time-hoppingsequence. The time-hopping sequence identifies a sub time slot of thesymbol value based time slots during which a pulse burst will begenerated.

In block 410, the symbol mapper 206 determines the polarities of thepulses to be generated during the pulse burst. The polarities of thepulses in the pulse burst are determined based on a chip scramblingsequence used to modulate the pulses.

In block 412, the pulse generator 208, generates a pulse burst inaccordance with the symbol location (derived from symbol value),time-hopping sequence, and polarity determined by the symbol mapper 206.

In block 414, the RF circuitry drives the signal generated by the pulsegenerator onto the antenna 212.

In block 416, a single guard interval is appended to the end of thetransmitted symbol. In at least some embodiments, the guard interval isa fixed time period that is determined based on maximum delay spread ofchannel. Consequently, the ratio of guard interval to symbol timedecreases as the data rate is decreased.

Tables 1 and 2 below summarize the power spectral density (“PSD”) forthe UWB band in various countries. The UWB low band (shown in Table 1)is not ideal for low-complexity BAN devices since regulations requiredevices that operate in this band support detection and avoidance(“DAA”) mechanisms, which increase complexity. If DAA is not supported,then devices operating the UWB low band must operate in a low duty cycle(“LDC”) mode, which does not allow the devices to support the higherdata rates, such as 1 Mbps. The UWB high band does not require eitherDAA, or LDC making the high band attractive for a low-complexityimplementation.

TABLE 1 UWB Low Band Frequency PSD Bands Remarks Australia N/A N/A N/AEU −41.3 dBm/MHz 3.1-4.8 GHz LDC or DAA is needed 4.2-4.8 GHz By Dec.31, 2010 Japan −41.3 dBm/MHz 3.4-4.8 GHz DAA is needed 4.2-4.8 GHz ByDec. 31, 2010 Korea −41.3 dBm/MHz 3.1-4.8 GHz LDC or DAA is needed4.2-4.8 GHz By Dec. 31, 2010 USA −41.3 dBm/MHz 3.1-10.6 GHz 

TABLE 2 UWB High Band Frequency Bands PSD Remarks Australia N/A N/A N/AEU   6-8.5 GHz −41.3 dBm/MHz Japan 7.25-10.25 GHz  −41.3 dBm/MHz Korea7.2-10.2 GHz −41.3 dBm/MHz USA 3.1-10.6 GHz −41.3 dBm/MHz Common7.25-8.5 GHz −41.3 dBm/MHz

Embodiments of the present disclosure use the frequency bands enumeratedin Table 3 for systems with 512 MHz bandwidth. Table 3 also shows theallocation of the frequency bands for various countries. The proposedfrequency bands were selected such that at least three non-overlapping512 MHz frequency bands are available in each country. The PHY cansupport four piconets per 512 MHz frequency band by using the IR-UWBmodulation scheme discussed above. Therefore, at least 12 piconets canbe supported in each country. The band plan or center frequencies of theselected frequency bands allow for a low-power transceiver architecture.

TABLE 3 Frequency Bands for 512 MHz Bandwidth Band Supported BandwidthLow Frequency Center High Frequency Number Region (MHz) (MHz) Frequency(MHz) (MHz) 1 US, EU 512 6400 6656 6912 2 US, EU 512 6912 7168 7424 3US, EU, Japan, Korea 512 7424 7680 7936 4 US, EU, Japan, Korea 512 79368192 8448 5 US, Japan, Korea 512 8448 8704 8960

Embodiments use the frequency bands enumerated in Table 4 for systemswith 528 MHz bandwidth. All the bands are located in the UWB high band,therefore no DAA mechanism need be implemented in the transceiver. Thefrequency bands are a part of WiMedia frequency bands (WiMediaBAND_ID=[7, 8, . . . , 14]). Advantageously, embodiments of BANtransceivers using the proposed frequency bands avoid partialfrequency-band overlap with WiMedia systems.

TABLE 4 Frequency Bands for 528 MHz Bandwidth Band Supported BandwidthLow Frequency Center High Frequency Number Region (MHz) (MHz) Frequency(MHz) (MHz) 1 US, EU 528 6336 6600 6864 2 US, EU 528 6864 7128 7392 3US, EU, Japan, Korea 528 7392 7656 7920 4 US, EU, Japan, Korea 528 79208184 8448 5 US, Japan, Korea 528 8448 8712 8976 6 US, Japan, Korea 5288976 9240 9504 7 US, Japan, Korea 528 9504 9768 10032 8 US 528 1003210296 10560

Table 5 gives exemplary system parameters for an uncoded system. Systemparameters are selected to provide an integer number of chips in a bursttime. Note that the parameters in this table can be modified to generateany number of data rates. The transmit (“Tx”) pulse shape listed belowis exemplary and other pulse shapes can be used.

TABLE 5 Exemplary Parameters for an Uncoded System Data rate (kbps),R_(b) 50 200 1000 2000 10039.21569 Modulation BPM-TH/DS BPM-TH/DSBPM-TH/DS BPM-TH/DS BPM-TH/DS FEC code rate, r 1 1 1 1 1 Symbol rate(ksps), R_(s) 50 200 1000 2000 10039.21569 Symbol period (ns), T_(s)20000 5000 1000 500 99.609375 Bandwidth, chip rate 512 512 512 512 512(MHz) Chip time (ns), T_(c) 1.953125 1.953125 1.953125 1.953125 1.953125Tx pulse shape root-raised root-raised root-raised root-raisedroot-raised cosine cosine cosine cosine cosine Guard interval (T_(c))128 64 32 24 15 Guard interval (ns), T_(GI) 250 125 62.5 46.87529.296875 Symbol period − GI (ns) 19750 4875 937.5 453.125 70.3125 #chips per symbol, N_(cps) 10240 2560 512 256 51 # chips in (symbol − GI)10112 2496 480 232 36 # bursts in symbol, 128 64 16 8 4 N_(burst) # ofchips in burst, N_(cpb) 79 39 30 29 9 Burst length (ns), T_(burst)154.296875 76.171875 58.59375 56.640625 17.578125 Average PRF in bust Tx4 8 32 64 128 region (MHz) Average PRF (MHz) 3.95 7.8 30 58 90.352941181/duty-cycle 129.6202532 65.64102564 17.06666667 8.827586207 5.666666667PRF: pulse repetition frequency

Table 6 gives exemplary system parameters for a coded system. (15,11)block code, e.g, BCH code, is assumed. Other types of codes and codingrates can be also be used and the table entries can be updatedaccordingly. System parameters are selected to have integer number ofchips in a burst time. Note that the parameters in this table can bemodified to generate any number of data rates. The transmit (“Tx”) pulseshape listed below is exemplary and other pulse shapes can be used.

TABLE 6 Exemplary Parameters for a Coded System, (15, 11) Block CodeData rate (kbps), R_(b) 50.00221956 200.0355177 1001.244444 2007.84313710147.74775 Modulation BPM-TH/DS BPM-TH/DS BPM-TH/DS BPM-TH/DS BPM-TH/DSFEC code rate, r 0.733333333 0.733333333 0.733333333 0.7333333330.733333333 Symbol rate (ksps), R_(s) 68.18484485 272.77570591365.333333 2737.967914 13837.83784 Symbol period (ns), T_(s)14666.01563 3666.015625 732.421875 365.234375 72.265625 Bandwidth, chiprate (MHz) 512 512 512 512 512 Chip time (ns), T_(c) 1.953125 1.9531251.953125 1.953125 1.953125 Tx pulse shape root-raised root-raisedroot-raised root-raised root-raised cosine cosine cosine cosine cosineGuard interval (T_(c)) 85 53 31 19 13 Guard interval (ns), T_(GI)166.015625 103.515625 60.546875 37.109375 25.390625 Symbol period − GI(ns) 14500 3562.5 671.875 328.125 46.875 # chips per symbol, N_(cps)7509 1877 375 187 37 # chips in (symbol − GI) 7424 1824 344 168 24 #bursts in symbol, N_(burst) 64 32 8 8 4 # of chips in burst, N_(cpb) 11657 43 21 6 Burst length (ns), T_(burst) 226.5625 111.328125 83.98437541.015625 11.71875 Average PRF in bust Tx 8 16 64 64 128 region (MHz)Average PRF (MHz) 7.909442003 15.54821524 58.70933333 57.497326283.02702703 1/duty-cycle 64.73275862 32.92982456 8.720930233 8.9047619056.166666667

Table 7 gives alternative exemplary system parameters for a codedsystem. Various code rates are shown. Other coding rates can be also beused and the table entries can be updated accordingly. System parametersare selected to have integer number of chips in a burst time. Note thatthe parameters in this table can be modified to generate any number ofdata rates.

TABLE 7 Exemplary Parameters for a Coded System Data rate (kbps), R_(b)113.5129 224.7092 523.3285 1015.8730 1918.8713 5264.0693 10070.3934Bandwidth, chip rate (MHz) 512 512 512 512 512 512 512 Chip time (ns),T_(c) 1.953125 1.953125 1.953125 1.953125 1.953125 1.953125 1.953125Modulation BPM-TH/DS BPM-TH/DS BPM-TH/DS BPM-TH/DS BPM-TH/DS BPM-TH/DSBPM-TH/DS FEC code rate, r 16/31 16/31 51/63 51/63 51/63 57/63 57/63 #bursts in symbol, N_(burst) 32 32 32 32 32 16 16 # hop bursts, N_(hop)16 16 16 16 16 8 8 # of chips in burst, N_(cpb) 72 36 24 12 6 4 2 Guardinterval (T_(c)) 24 24 24 24 24 24 14 # chips per symbol, N_(cps) 23281176 792 408 216 88 46 Burst length (ns), T_(burst) 140.6250 70.312546.8750 23.4375 11.7188 7.8125 3.9063 Guard interval (ns), T_(GI)46.8750 46.8750 46.8750 46.8750 46.8750 46.8750 27.3438 Symbol period(ns), T_(s) 4546.8750 2296.8750 1546.8750 796.8750 421.8750 171.875089.8438 Symbol rate (ksps), R_(s) 219.9313 435.3741 646.4646 1254.90202370.3704 5818.1818 11130.4348 Average PRF (MHz) 15.8351 15.6735 15.515215.0588 14.2222 23.2727 22.2609 1/duty-cycle 32.3333 32.6667 33.000034.0000 36.0000 22.0000 23.0000

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. For example, while embodiments ofthe present disclosure have been presented in the context of body areanetworks, those skilled in the art of wireless communications willunderstand that the disclosed modulation system is applicable variouswireless applications. It is intended that the following claims beinterpreted to embrace all such variations and modifications.

What is claimed is:
 1. A symbol modulation system, comprising: a symbolmapper configured to: determine, based on a value of a symbol and avalue of a time-hopping sequence, a time within a predetermined symboltransmission interval at which a transmission representative of thesymbol will occur; and generate a single guard interval within thesymbol transmission interval; wherein the time is selected from aplurality of symbol value based time slots, and a plurality oftime-hopping sequence sub-time-slots within each symbol value based timeslot; and wherein the single guard interval is positioned to terminatethe symbol transmission interval.
 2. The symbol modulation system ofclaim 1, wherein the symbol mapper is configured to increase the ratioof the single guard interval to the symbol transmission interval as thedata rate increases.
 3. The symbol modulation system of claim 1, whereinthe symbol mapper is configured to determine a polarity of each pulse ofa plurality pulses generated during the determined transmission time. 4.The symbol modulation system of claim 1, wherein the modulation systemis configured to generate the symbol transmission interval as a sum ofthe time of the single guard interval and a product of an order of thesymbol, a number of hops in a time-hopping sequence, a number of chipsper sub-time-slot, and time per chip.
 5. The symbol modulation system ofclaim 1, wherein the symbol mapper is configured to generate guardintervals within the predetermined symbol transmission interval thatoccupy less than half of the predetermined symbol transmission interval.6. The symbol modulation system of claim 1, wherein the modulationsystem is configured to transmit over a 528 mega-hertz (“MHz”) bandwidthhaving a center frequency in a range of 6.600 giga-hertz (“GHz”) to10.296 GHz.
 7. The symbol modulation system of claim 6, wherein themodulation system is configured to operate at center frequenciesselected from a group consisting of 6.600 GHz, 7.128 GHz, 7.656 GHz,8.184 GHz, 8.712 GHz, 9.240 GHz, 9.768 GHz, and 10.296 GHz.
 8. Thesymbol modulation system of claim 1, wherein the modulation system isconfigured to transmit over a 512 MHz bandwidth having a centerfrequency in a range of 6.656 GHz to 8.704 GHz.
 9. The symbol modulationsystem of claim 8, wherein the modulation system is configured tooperate at center frequencies selected from a group consisting of 6.656GHz, 7.168 GHz, 7.680 GHz, 8.192 GHz, and 8.704 GHz.
 10. A method,comprising: determining, by a symbol mapping circuit, based on a valueof a symbol to be transmitted and a value of a time-hopping sequence, atime within a predetermined symbol transmission interval at which aburst of pulses representative of the symbol will be occur; generating,by the symbol mapping circuit, a single guard interval that terminatesthe transmission interval; wherein the determined time is selected froma plurality of symbol value based time slots, and a plurality oftime-hopping sequence sub-time-slots within each symbol value based timeslot.
 11. The method of claim 10, wherein generating the single guardinterval comprises decreasing a ratio of the guard interval to thetransmission interval as a data rate applied to the burst of pulsesrepresentative of the symbol decreases.
 12. The method of claim 10,further comprising determining, by the symbol mapping circuit, apolarity of each of a plurality of pulses of the burst of pulses. 13.The method of claim 10, wherein the entire predetermined symboltransmission interval, less the single guard interval, is subdividedinto a plurality of equal time slots, each slot configured fortransmission of the burst of pulses representative of the symbol. 14.The method of claim 10, further comprising transmitting the value of thesymbol over a 528 mega-hertz (“MHz”) bandwidth having a center frequencyselected from a group of center frequencies consisting of 6.600giga-hertz (“GHz”), 1.7128 GHz, 7.656 GHz, 8.184 GHz, 8.712 GHz, 9.240GHz, 9.768 GHz, and 10.296 GHz.
 15. The method of claim 10, furthercomprising transmitting the value of the symbol over a 512 MHz bandwidthhaving a center frequency selected from a group of center frequenciesconsisting of 6.656 GHz, 7.168 GHz, 7.680 GHz, 8.192 GHz, and 8.704 GHz.16. A symbol modulation system, comprising: a symbol mapper configuredto: determine, based on a value of a time-hopping sequence, a timewithin a predetermined symbol transmission interval at which a signalburst representative of the symbol will be transmitted; determine, basedon a value of the symbol, a modulation factor to apply to the signalburst during the time; and generate a single guard interval within thesymbol transmission interval; wherein the time is selected from aplurality of time-hopping sequence time-slots within the predeterminedsymbol transmission interval; and wherein the single guard interval ispositioned to terminate the symbol transmission interval.
 17. The symbolmodulation system of claim 16, wherein the symbol mapper is configuredto select the modulation factor based on a modulation scheme selectedfrom a group consisting of on/off keying, pulse amplitude modulation,phase-shift keying; and differential phase-shift keying.
 18. The symbolmodulation system of claim 16, wherein the symbol mapper is configuredto increase the ratio of the single guard interval to the symboltransmission interval as the data rate increases.
 19. The symbolmodulation system of claim 16, wherein the symbol mapper is configuredto determine a polarity of each pulse of a plurality pulses generatedduring the determined transmission time.
 20. The symbol modulationsystem of claim 16, wherein the modulation system is configured togenerate the symbol transmission interval as a sum of the time of thesingle guard interval and a product of a number of hops in atime-hopping sequence, a number of chips per sub-time-slot, and time perchip.
 21. The symbol modulation system of claim 16, wherein themodulation system is configured to transmit over one of a 512 MHzbandwidth having a center frequency in a range of 6.656 GHz to 8.704 GHzand a 528 mega-hertz (“MHz”) bandwidth having a center frequency in arange of 6.600 giga-hertz (“GHz”) to 10.296 GHz.